In audio systems, echo interference cannot be avoided due to a signal reflection path. In audio communications, echoes generally classified to electric echoes and acoustic echoes. Electric echoes are caused by signal reflection which is generated due to impedance mismatch. Acoustic echoes are generally generated in below scenario. At a receptor side, voice from a speaker is received by a voice receiving device and then sent to a speaker side. The acoustic echoes include direct echo and indirect echo. The voice which comes from the speaker and then directly received by the voice receiving device is called the direct echo. The voice which comes from the speaker are reflected for one or more than one time through different paths (for example, buildings or any objects in buildings) and then all the reflected voice is received by the voice receiving device, which is called the indirect echo. Echoes are sent to the speaker side after channel delay and heard by a speaker at the speaker side, which causes interference to audios at the speaker side, reduces audio clearness, and affects audio communication quality.
In the sixties of the 20th century, to eliminate the influence to audio communications caused by echoes, Sondhi in Bell Labs raised a self-adaptive filtering method to realize echo cancellation. FIG. 1 schematically illustrates a block diagram of a self-adaptive echo cancellation system. Referring to FIG. 1, before being played out by a speaker 1 in a near terminal, a downlink reference signal that comes from a remote terminal forms an electric echo through an electric echo path 2. After the downlink reference signal is played out by the speaker 1, the played out signal is absorbed by a microphone through an acoustic echo path 3, to form an acoustic echo. A self-adaptive filter 4 performs filtering to the downlink reference signal using an echo path model 5. An output signal of the filtering (namely, a cancellation signal) may cancel the echoes, and a residual signal (namely, an error signal) after the cancellation is sent to the remote terminal. Besides, a self-adaptive filtering algorithm 6 adjusts parameters of the echo path model 5 using the downlink reference signal and the residual signal, to reduce residual echoes gradually.
In echo cancellation technologies, as acoustic echoes have features such as multi-path, long delay, slow attenuation, time variation and nonlinear, acoustic echo cancellation (AEC) has strict requirements on the performance of the self-adaptive filter 4. To a handheld device which is seriously nonlinear, the requirements on the self-adaptive filter 4 may be stricter. As a handheld device is relatively small, a micro speaker therein is much smaller than a normal speaker. To satisfy volume requirement in hands-free communication, the micro speaker generally works in a nonlinear region, which results in more serious audio distortion. In this situation, the self-adaptive filter 4 may provide very small echo loss and works unsteadily. The self-adaptive filter 4 may provide no echo loss when facing a transient signal. Therefore, a method and apparatus for reducing distortion echo, which can steadily provide echo loss with high amplitude under a situation that a speaker has relatively serious distortion, are required.